Radiometric Dating of tephras from Pre-caldera and Caldera-forming stages, Towada volcano, Northeast Japan

Towada volcano is an active volcano located in the northern part of the Northeast Japan arc. We carried out fission-track (FT) and AMS radiocarbon (¹⁴C) dating of tephras from Towada and Hakkoda volcanoes to establish a detailed eruptive history during the Pre-caldera and Caldera-forming stages of Towada volcano. The obtained FT ages were 0.23 ± 0.05 Ma for Shirobeta tephra (WP), 0.19 ± 0.05 Ma for T-6 tephra, 0.08 ± 0.03 Ma for Zarame 1 tephra (ZP1), and 0.09 ± 0.03 Ma for Okuse Pyroclastic Flow Deposits. Although these FT ages are consistent with stratigraphy, they have large error ranges of several tens of thousands of years. Therefore, further examinations including application of other chronological dating methods are necessary to obtain more precise estimates of the eruptive age of these tephras. The obtained ¹⁴C age was 17,730 ± 70 BP for Biscuit 2 tephra (BP2). Based on stratigraphical consistency, this ¹⁴C age is appropriate for the eruptive age of BP2. (author)